Most vehicles powered by an internal combustion engine waste a considerable amount of fuel during periods when the vehicle is stopped and the engine is idling. For vehicles like refuse trucks, the idling engine is frequently used to drive auxiliary hydraulic systems when the vehicle is stopped, namely the hydraulic arm that picks up curb-side trash bins, and the hydraulic compactor that compresses the trash in the truck. However, the power required to perform this work is relatively low and a significant portion of the fuel consumed while the engine is idling is mainly used to overcome internal friction in the engine, which results in a very low fuel efficiency during the typical duty cycle of a refuse truck.
Even though the auxiliary hydraulic system may not be required for each stop, or the auxiliary hydraulic system could be powered independently of the engine, it would not be an acceptable option to turn off the engine of a typical OEM refuse truck each time the truck was stopped at a collection point. For one thing, the starting motor of such trucks would undoubtedly suffer premature wear if used to restart the engine as many as one thousand times per day or more, which is the normal duty cycle for a refuse truck.
Moreover, many refuse trucks are equipped with an automatic transmission having a hydraulic shifting mechanism. The hydraulic pressure in the transmission is supplied by a pump that is integrated within the transmission but driven by the internal combustion engine. When the internal combustion engine is turned off, the transmission pump stops supplying pressure to the transmission and as a result, the transmission automatically shifts from drive into neutral. When the internal combustion engine is restarted, a period of time is needed to rebuild hydraulic pressure in the transmission, which delays the ability to shift the transmission into drive. Such a delay would be frustrating to the operator of the truck; the delay could also be potentially dangerous as there would be a risk that the truck could roll back if it were stopped on an upward slope.
The power steering system of typical vehicles also does not work when the engine is turned off as the power steering fluid pump is as well driven by the internal combustion engine.